This invention provides novel devices, systems, and methods for delivering small interfering RNA to targeted sites in the brain to inhibit or arrest the development and progression of neurodegenerative disorders. For several neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease, Huntington's disease, Spinocerebellar Ataxia Type 1, Type 2, and Type 3, and dentatorubral pallidoluysian atrophy (DRLPA), proteins involved in the overall pathogenic progression of the disease have been identified. There is currently no cure for these neurodegenerative diseases. These diseases are progressively debilitating and most are ultimately fatal.
Further problematic of these neurodegenerative diseases (especially Alzheimer's disease and Parkinson's disease) is that their prevalence continues to increase, thus creating a serious public health problem. Recent studies have pointed to alpha-synuclein (Parkinson's disease), beta-amyloid-cleaving enzyme 1 (BACE1 (including variants thereof, e.g. variants A, B, C, and D)) (Alzheimer's disease), huntingtin (Huntington's disease), and ataxin 1 (Spinocerebellar Ataxia Type 1) as major factors in the pathogenesis of each of these diseases, respectively.
The neurodegenerative process in Parkinson's disease and Alzheimer's disease is characterized by extensive loss of selected neuronal cell populations accompanied by synaptic injury and astrogliosis. Pathological hallmarks of Alzheimer's disease include formation of amyloid plaques, neurofibrillary tangles and neuropil thread formation; pathological hallmarks of Parkinson's diseases include the formation of intraneuronal inclusions called Lewy bodies and the loss of dopaminergic neurons in the substantia nigra. Although the mechanisms triggering cell dysfunction and death are unclear, the prevailing view is that neurodegeneration results from toxic effects subsequent to the accumulation of specific neuronal cell proteins, such as alpha-synuclein (Parkinson's disease) and amyloid precursor protein (APP) (Alzheimer's disease—processed into beta-amyloid by BACE1 (including variants thereof, e.g. variants A, B, C, and D)).
Alpha-synuclein has been implicated in Parkinson's disease because it is abundantly found in Lewy Bodies, its overexpression in transgenic mice leads to Parkinson's disease-like pathology, and mutations within this molecule are associated with familial Parkinson's disease. Alpha-synuclein, which belongs to a larger family of molecules including beta and gamma-synuclein, is a 140 amino acid non-amyloid synaptic protein which is a precursor of the 35 amino acid non-amyloid component protein found in amyloid plaques.
Alzheimer's disease is a progressive degenerative disorder of the brain characterized by mental deterioration, memory loss, confusion, and disorientation. Among the cellular mechanisms contributing to this pathology are two types of fibrillar protein deposits in the brain: intracellular neurofibrillary tangles composed of polymerized tau protein, and abundant extracellular fibrils comprised largely of beta-amyloid. Beta-amyloid, also known as Abeta, arises from the proteolytic processing of the amyloid precursor protein (APP) at the beta- and gamma-secretase cleavage sites giving rise to the cellular toxicity and amyloid-forming capacity of the two major forms of Abeta (Abeta40 and Abeta42). Thus, preventing APP processing into plaque-producing forms of amyloid may critically influence the formation and progression of the disease making BACE1 (including variants thereof, e.g. variants A, B, C, and D) a clinical target for inhibiting or arresting this disease. Similar reports suggest presenilins are candidate targets for redirecting aberrant processing.
Huntington's disease is a fatal, hereditary neurodegenerative disorder characterized by involuntary “ballistic” movements, depression, and dementia. The cause has been established to be a mutation in a single gene consisting of an excessively long series of C, A, G, C, A, G, . . . C, A, G, nucleotides in the DNA. The CAG repeat is in the region of the gene that codes for the protein the gene produces. Thus, the resulting huntingtin protein is also “expanded,” containing an excessively long region made of the amino acid glutamine, for which “CAG” encodes. Shortly after this mutation was pinpointed as the cause of Huntington's disease, similar CAG repeat expansions in other genes were sought and found to be the cause of numerous other fatal, hereditary neurodegenerative diseases. The list of these so-called “polyglutamine” diseases now includes at least eleven more, including: spinocerebellar ataxia type 1, type 2, and type 3, spinobulbar muscular atrophy (SBMA or Kennedy's disease) and dentatorubral-pallidoluysian atropy (DRPLA). Although the particular gene containing the expanded CAG repeat is different in each disease, it is the production of an expanded polyglutamine protein in the brain that causes each one. Symptoms typically emerge in early to middle-aged adulthood, with death ensuing 10 to 15 years later. No effective treatments for these fatal diseases currently exist.
There is considerable evidence suggesting that shutting off production of the abnormal protein in neurons will be therapeutic in polyglutamine diseases. The cause of these diseases is known to be the gain of a new function by the mutant protein, not the loss of the protein's original function. Mice harboring the human, expanded transgene for spinocerebellar ataxia type 1 (SCA1) become severely ataxic in young adulthood (Clark, H., et al., Journal of Neuroscience 17: 7385-7395 (1997)), but mice in which the corresponding mouse gene has been knocked out do not suffer ataxia or display other major abnormalities (Matilla, A., et al., Journal of Neuroscience 18: 5508-5516 (1998)). Transgenic mice for SCA1 in which the abnormal ataxin1 protein is produced but has been genetically engineered to be incapable of entering the cell's nucleus do not develop ataxia (Klement, I., et al., Cell 95: 41-53 (1998)). Finally, a transgenic mouse model of Huntington's disease has been made in which the mutant human transgene has been engineered in a way that it can be artificially “turned off” by administering tetracycline (Normally, in mice and humans, administration of this antibiotic would have no effect on the disease). After these mice have begun to develop symptoms, shutting off production of the abnormal protein production by chronic administration of tetracyclin leads to an improvement in their behavior (Yamamoto, A., et al., Cell 101: 57-66 (2000)). This suggests that reducing expression of the abnormal huntingtin protein in humans might not only prevent Huntington's disease from progressing in newly diagnosed patients, but may improve the quality of life of patients already suffering from its symptoms.
Various groups have been recently studying the effectiveness of siRNAs. Caplen, et al. (Human Molecular Genetics, 11(2): 175-184 (2002)) assessed a variety of different double stranded RNAs for their ability to inhibit cell expression of mRNA transcripts of the human androgen receptor gene containing different CAG repeats. Their work found gene—specific inhibition occurred with double stranded RNAs containing CAG repeats only when flanking sequences to the CAG repeats were present in the double stranded RNAs. They were also able to show that constructed double stranded RNAs were able to rescue caspase-3 activation induced by expression of a protein with an expanded polyglutamine region. Xia, Mao, et al. (Nature Biotechnology, 20: 1006-1010 (2002)) demonstrated the inhibition of polyglutamine (CAG) expression of engineered neural PC12 clonal cell lines that express a fused polyglutamine-fluorescent protein using constructed recombinant adenovirus expressing siRNAs targeting the mRNA encoding green fluorescent protein.
The design and use of small interfering RNA complementary to mRNA targets that produce particular proteins is a recent tool employed by molecular biologists to prevent translation of specific mRNAs. Other tools used by molecular biologists to interfere with protein expression prior to translation involve cleavage of the mRNA sequences using ribozymes against therapeutic targets for Alzheimer's disease (see WO01/16312A2) and Parkinson's disease (see WO99/50300A1 and WO01/60794A2). However, none of the above aforementioned patents disclose methods for the specifically localized delivery of small interfering RNA vectors to targeted cells of the brain in a manner capable of local treatment of neurodegenerative diseases. The above patents do not disclose use of delivery devices or any method of delivery or infusion of small interfering RNA vectors to the brain. For example, the above patents do not disclose or suggest a method of delivery or infusion of small interfering RNA vectors to the brain by an intracranial delivery device.
Further, the foregoing prior art does not disclose any technique for infusing into the brain small interfering RNA vectors, nor does the prior art disclose whether small interfering RNA vectors, upon infusion into the brain, are capable of entering neurons and producing the desired small interfering RNA, which is then capable of reducing production of at least one protein involved in the pathogenesis of neurodegenerative disorders.
The prior art describes direct systemic delivery of ribozymes. This approach for treatment of neurodegenerative disorders would appear neither possible nor desirable. First, interfering RNAs are distinctly different than ribozymes. Second, small RNA molecules delivered systemically will not persist in vivo long enough to reach the desired target, nor are they likely to cross the blood-brain barrier. Further, the approach taken by the prior art may be impractical because of the large quantity of small interfering RNA that might have to be administered by this method to achieve an effective quantity in the brain. Even when the blood-brain barrier is temporarily opened, the vast majority of oligonucleotide delivered via the bloodstream may be lost to other organ systems in the body, especially the liver.
U.S. Pat. Nos. 5,735,814 and 6,042,579 disclose the use of drug infusion for the treatment of Huntington's disease, but the drugs specifically identified in these patents pertain to agents capable of altering the level of excitation of neurons, and do not specifically identify agents intended to enter the cell and alter protein production within cells.
The present invention solves prior problems existing in the prior art relating to systemic delivery of nucleic acids by directly delivering small interfering RNA in the form of DNA encoding the small interfering RNA to target cells of the brain using viral vectors. Directed delivery of the small interfering RNA vectors to the affected region of the brain infusion overcomes previous obstacles related to delivery. Further, use of viral vectors allows for efficient entry into the targeted cells and for efficient short and long term production of the small interfering RNA agents by having the cells' machinery direct the production of the small interfering RNA themselves. Finally, the present invention provides a unique targeting and selectivity profile by customizing the active small interfering RNA agents to specific sites in the mRNA coding sequences for the offending proteins.